Metallic Coated Cores to Facilitate Thin Wall Casting

ABSTRACT

A core for investment casting processes includes a core having one or more ceramic materials; and an exterior layer of metal material not susceptible to oxidation under investment casting operating conditions. A method for casting a turbine engine component having an internal passageway includes the steps of forming one or more mold sections each having internal surfaces and at least one of the aforementioned cores for forming one or more turbine engine components having at least one internal passageway; assembling the one or more mold sections; introducing a molten alloy into the one or more assembled mold sections; and consuming the metal of the at least one core during the process.

CROSS-REFERENCE TO RELATED APPLICATION

This is a divisional application of Ser. No. 11/343,369, filed Jan. 30,2006, and entitled “Metallic Coated Cores to Facilitate Thin WallCasting”, the disclosure of which is incorporated by reference herein inits entirety as if set forth at length.

FIELD OF USE

The present disclosure relates to investment casting and, moreparticularly, relates to thin wall casting.

BACKGROUND OF THE INVENTION

Investment casting is a commonly used technique for forming metalliccomponents having complex geometries, especially hollow components, andis used in the fabrication of superalloy gas turbine engine componentssuch as blades and vanes and their hollow airfoils.

Advanced airfoil designs have very thin metal walls and complex coolingpassages. Depending upon the size of the features to be cast, thesecooling passages are formed either with ceramic mini-cores and/orrefractory metal cores. The combined features make the cooling passagesextremely difficult to cast successfully due to the high surface area ofceramic in relation to the amount of metal in the thin wall areas.Ceramic to molten metal contact has a high surface tension associatedwith such contact. The ceramic does not ‘wet out’ easily leading tonon-fill defects.

Consequently, there exists room for improvements in the investmentcasting process.

SUMMARY OF THE INVENTION

In accordance with the present disclosure, a core for investment castingprocesses broadly comprises a core comprising one or more ceramicmaterials, one or more refractory metal cores, or both said ceramicmaterials and said refractory metal cores; and an exterior layer of ametal compatible with a casting material.

In accordance with another aspect of the present disclosure, a methodfor casting a turbine engine component having an internal passagewaycomprises forming one or more mold sections each having internalsurfaces and at least one core comprising a layer of a metal compatiblewith a casting material for forming one or more turbine enginecomponents having at least one internal passageway; assembling the oneor more mold sections; introducing a molten alloy into the one or moreassembled mold sections; and consuming the layer of the metal of the atleast one core.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a representation of a metal coated core of the presentinvention; and

FIG. 2 is a representation of an investment casting process employingthe metal coated cores of FIG. 1.

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION

The present article(s) and method(s) described herein are intended tofacilitate the casting of complex structural features while reducingpart defects associated with the failure to “wet out” due to surfacetension between ceramic to molten metal contact. The present methodinvolves coating ceramic cores and refractory metal cores with a metalcontaining material prior to the wax injection operation of theinvestment casting process. The metal coating prevents the ceramic tomolten metal contact during the process, and instead provides a metal tometal contact to which a much lower surface tension is associated thanceramic to molten metal contact. The lower surface tension facilitatesthe filling of the thin wall features, e.g., complex cooling passages,and reduces part variations and defects.

Referring now to FIG. 1, a core 10 for use in investment castingprocesses is shown. Core 10 generally comprises a substantiallycylindrical shape composed of one or more ceramic materials known to oneof ordinary skill in the art, one or more refractory metal core (“RMC”)materials known to one of ordinary skill in the art, and combinations ofboth ceramic and RMC materials. For example, the ceramic materials mayinclude, but are not limited to, silica based, alumina based, mixturescomprising at least one of the foregoing ceramic materials, and thelike. The RMC materials may include, but are not limited to, molybdenum,niobium, tantalum, tungsten, and the like. As known to one of ordinaryskill in the art, such RMC materials may include a protective ceramiccoating such as silica, alumina, zirconia, chromia, mullite and hafniato prevent oxidation and erosion by molten metal.

An exterior layer 12 comprising a metal material may be disposed aboutthe exterior surface of the core 10. The exterior layer may be along theceramic of a ceramic core or of the protective coating on an RMC as isdiscussed further below. In the particular illustrated example, the core10 is an RMC with a protective ceramic coating 14 between the core 10and the exterior layer 12. The metal material generally comprises ametal not susceptible to oxidation under investment casting operatingconditions. For example, the metal material of the exterior layer 12 maycomprise a noble metal such as, but not limited to, gold, platinum andcombinations comprising at least one of the foregoing noble metals.Preferably, the metal selected is compatible with the molten metal beingcast to form the molded part.

The exterior layer 12 generally possesses a thickness sufficient toprovide the desired metal to metal contact as known to one of ordinaryskill in the art. The metal of the exterior layer 12 may be applied byany one of a number of deposition techniques known to one of ordinaryskill in the art. For example, the metal may be sputtered onto core 10to form the exterior layer 12 using any number of sputtering techniquesknown to one of ordinary skill in the art. Or, in another example, themetal may be plated onto core 10 to form the exterior layer 12 using anynumber of plating techniques known to one of ordinary skill in the art.As known to one of ordinary skill in the art, sputtering techniquesproduce a very thin layer, for example, ten-thousandths of an inch tohundred-thousandths of an inch in thickness. And, plating techniques arealso capable of producing a layer of comparable thickness. As described,the metal compatible with a casting material may comprise a noble metaland/or a metal selected from Group VIII, Group VIIIA and Group IB of thePeriodic Table of Elements as shown in the Handbook of Chemistry andPhysics, CRC Press, 71^(st) ed., p. 1-10 (1990-91). It is alsocontemplated that additional metals may be employed when an inertatmosphere, such as a noble gas, is utilized when applying the exteriorlayer 12 to the core 10.

As described above, the exterior layer 12 of metal material preventsceramic to molten metal contact during the investment casting process,and instead provides a metal to metal contact with which a much lowersurface tension is associated. The lower surface tension facilitates thefilling of the thin wall features, e.g., complex cooling passages, andreduces part variations and defects.

The metal coated cores 10 may be utilized in any investment castingprocess known to one of ordinary skill in the art. More particularly,the metal coated cores 10 may be utilized whenever parts having hollowinteriors are being cast. For purposes of illustration, and not to betaken in a limiting sense, FIG. 2 shows an exemplary sequence of stepsfor using the metal coated cores 10 described herein in an investmentcasting process. A wax pattern is formed 40 over the core(s).

A shell-forming coating may be applied 44 in one or more steps involvingcombinations of wet or dry dipping and wet or dry spraying.

After a final drying, the wax may be removed via a dewax process 46 suchas in a steam autoclave. After the dewax process, the shell may then betrimmed 48 and minor defects in the shell may be patched. The shell maybe fired 54 to strengthen the shell and may be seeded 56 if required toform a predetermined crystallographic orientation. The shell may then beinstalled 58 in the casting furnace and the molten metal introduced 60.The molten metal consumes the exterior metal material layer 12 of metalcoated core 10 which simultaneously facilitates the intended metal tometal contact and desired reduced surface tension. After cooling 62 ofthe metal, the metal part(s) may be deshelled 64. Machining 66 mayseparate the parts from each other, remove additional surplus material,and provide desired external and internal part profiles. Post machiningtreatments 68 may include heat or chemical treatments, coatings, or thelike.

The metal coated cores and method(s) utilizing said cores describedherein provides a significant advantage over non-metal coated cores andtheir methods of use of the prior art. The metal coating describedherein prevents the ceramic to molten metal contact during theinvestment casting process, and instead provides a metal to metalcontact to which a much lower surface tension is associated. The lowersurface tension facilitates the filling of the thin wall features, e.g.,complex cooling passages, and reduces part variations and defects. Byemploying metal coated cores in investment casting processes, thinwalled, hollow parts having complex features may be cast consistentlywith such results being reproducible.

It is to be understood that the invention is not limited to theillustrations described and shown herein, which are deemed to be merelyillustrative of the best modes of carrying out the invention, and whichare susceptible to modification of form, size, arrangement of parts, anddetails of operation. The invention rather is intended to encompass allsuch modifications which are within its spirit and scope as defined bythe claims.

1. A core for investment casting processes, comprising: one or moreceramic materials; and a layer of metal atop the one or more ceramicmaterials.
 2. The core of claim 1, wherein said one or more ceramicmaterials are selected from the group consisting of silica based ceramicmaterials, alumina based ceramic materials and combinations thereof. 3.The core of claim 1, wherein the one or more ceramic materials form aceramic coating atop one or more refractory metal cores.
 4. The core ofclaim 3, wherein said one or more refractory metal cores are selectedfrom the group consisting of molybdenum, niobium, tantalum and tungsten.5. The core of claim 1, wherein said ceramic material comprises amaterial selected from the group consisting of silica, alumina,zirconia, chromia, mullite and hafnia.
 6. The core of claim 1, whereinsaid metal comprises a noble metal.
 7. The core of claim 1, wherein saidmetal comprises a metal selected from the group consisting of GroupVIII, Group VIIIA and Group IB.
 8. The core of claim 1, wherein saidexterior layer of said metal is a layer of sputtered metal material. 9.The core of claim 1, wherein said layer of said metal is a layer ofplated metal material.
 10. A method for casting a turbine enginecomponent having an internal passageway, comprising: forming one or moremold sections each having internal surfaces and at least one corecomprising a layer of metal compatible with a casting material forforming one or more turbine engine components having at least oneinternal passageway, said layer of metal atop one or more ceramicmaterials; introducing a molten alloy into the one or more assembledmold sections; and consuming said layer of said metal of said at leastone core.